The mobile casual gaming worldwide market has the potential to reach $7.5 billion by 2015. Smartphone usage is on the rise and so is the prevalence of mobile gaming, according to a report from SuperData.

Asia is currently the largest mobile gaming market, followed closely by the United States. Even though this install base is large, simple feature phones still dominate at a whopping 85 percent.

What’s most interesting in SuperData’s findings is how much money is spent on freemium games that allow players to pay small amounts over time for temporary unlockable items. Female gamers ages 25-34 spend an average of $12.92 a month on micro-transactions which is $5.12 more than men in the same age group.

While in-app purchases are on the rise, ad revenue is still the major money-maker for mobile products. Angry Birds on Android makes $1-6 million per month purely from ads.

Update: Tiny Tower data removed as NimbleBit has never officially released that information.